The wheels of wheeled vehicles are mounted towards the vehicle chassis on suspensions, whose task is to provide for the vehicle a support towards the driving surface, which enables a spring supported and simultaneously damped mounting of the spring loaded section of the vehicle on the terrain, and with regard to the driving wheel, the suspensions secure a transmission of the driving force to the driving surface.
Each suspension is formed of a kinematic system of rigid bodies, which ensures a definite guidance of the wheel toward the vehicle chassis, and of spring and damping means, which ensure a dynamic transmission of force reaction induced between the driving surface and the travelling wheel on the vehicle chassis. There exists a great number of kinematic schemes in suspension of wheels. The currently used suspensions, for example parallelogram, trapezoidal, telescopic (McPherson), pendulous, crank, and angle suspensions, are characterized by both positive and negative specific characteristics. The basic requirement is minimum changes in geometry of the undercarriage at springing action, i.e. at a deflection of the suspension from the nominal position. The changes in geometry are mostly the changes in wheel gauge and in wheel base and the change in position of the side plane of the wheel with respect to the vertical longitudinal symmetry plane of vehicle.
For vehicles designated for driving on roads the change of these parameters is small, which is given by low values of expected springing action. Minor driving surface irregularity does not require the application of spring and damping means allowing large displacements, where the extreme positions of suspensions towards the vehicle chassis are defined by means of bumpy stops.
Another situation exists for vehicles destined for operation outside roads in a free terrain, where a great travel in suspension is one of the basic required characteristics of the vehicle undercarriage. The geometry of kinematic arrangements of the known types of suspensions by itself enables great travel without problems. The limiting elements in this section of the undercarriage are the spring of the suspension and the shock absorber of the suspension, quite frequently these means being integrated into the spring and damping unit.
Extreme positions of the axle are illustrated on an example of a crank suspension of a rear rigid axle being suspended by means of a central spring and damping unit mounted in a vertical longitudinal symmetry plane of a terrain vehicle (FIGS. 1a, 1b). It is apparent that the working travel of the spring, as limited by its extreme positions, is very short by which it restricts the wheel travel. Such an arrangement is practically not applicable for an off-road vehicle.
In principle, the background art proposes two solutions to this problem.
The first design, at the same positioning of the lower end of the spring and damping unit on the crank of the suspension, utilizes a longer spring with a greater number of coils. Having not changed the diameter of the wire and the spring, its rigidity is reduced while at the same time a greater travel is enabled. Nevertheless the long spring is unstable in a side direction, which complicates the stress on the spring and reduces the spring life. Simultaneously, mounting of an upper end of the long spring and damping unit causes structural problems from the point of view of space requirements.
The second solution utilizes a short spring. In this case it is necessary to transfer the connection of the lower end of the spring and damping unit to the crank of the suspension closer to the axis of crank rotation. In this case the stress on the spring increases substantially, therefore the spring must be made of a thicker wire. High rigidity of the spring increases bending stress of the crank, causing an increase in the crank dimensions. Through this the unsuspended mass of the axle is increased with negative consequences to controlling comfort. None of these solutions remedies the basic problem, which is the loss of adhesion and thus loss of the propulsive effect of the axle in an area of maximum extension of the spring and damping unit, when the force produced by the spring is the smallest. In the contrary situation of a minimum length of the spring and damping unit the forces transferred into the structure of vehicle are extremely great and require a huge dimensioning of the adjacent parts of vehicle.
The goal of the invention is to eliminate or at least reduce shortcomings of the background art, first of all through the structural arrangement to better use the possibilities, which are provided by the spring for suspension of a vehicle.